In the operation of rotating assemblies the performance capabilities such as rotational speed, ability to carry axial, transverse, and torque loads, permissible operating temperatures, permissible temperature changes, and useful life, are limited by many factors. Also, rotating assemblies which are designed to meet high-level performance requirements will in general be more demanding in terms of manufacturing tolerances, difficulty of original assembly, and difficulty of disassembly and re-assembly for the purpose of repair.
In particular, in fitting a ball bearing into place between a shaft and a housing which are to be supported for relative rotation, it has been customary to make the bearing assembly as precisely concentric as possible, with respect to both the shaft and the housing. It is extremely important to prevent rotation of the inner and outer rings of the ball bearing relative to the shaft and housing with which they are respectively associated. Established industry practice has mandated precise tolerances for the outer cylindrical surface of the shaft, the inner cylindrical surface of the shaft housing, and the inner and outer cylindrical surfaces of the inner and outer rings, respectively, of the ball bearing. Furthermore, assembly procedures have been difficult and time-consuming, both during original manufacture and during repair procedures, because the ball bearing must be mated to both the shaft and the housing. An interference fit is required between one ring and the rotating member (housing or shaft) while a sliding fit is required between the other ring and the stationary or non-rotating member (shaft or housing). In certain applications, however, an interference fit is required for both members.
It has long been understood that construction of a precise assembly has a natural enemy in the form of expansions and contractions of the various component parts which necessarily occur during operation of the mechanism, because of temperature changes that result from the operation and because of thermal expansion of the material or materials used to construct the assembly. Thus, it has been common practice to include in a rotary assembly certain parts whose sole purpose is to provide temperature compensation.
For example, in a rotary assembly the operating temperatures may cause the shaft to elongate much more than the housing, or vice versa. Since the shaft is usually supported from two or more bearing assemblies which are axially separated, there has to be an axial adjustment of the position of all but one of the bearing assemblies in order to accommodate the temperature change. It is therefore common practice to utilize a spring means in conjunction with a ball bearing, to maintain the axial position of the bearing with respect to one of the shaft or housing.
An additional problem is that wear of the parts of a rotating assembly changes the original dimensions, and hence the operating characteristics, including the manner in which those characteristics are affected by temperature changes.